A schematic for either the Lenovo or IBM hardware is a precise technical artifact. Understanding its typical structure can make the search more efficient and help interpret results once found.
Small-profile design for ultraportable "Slim" series laptops. bm5291 ver 1.3 schematic
on the schematic (e.g., PU401 for a buck regulator). A schematic for either the Lenovo or IBM
Look for Transient Voltage Suppressors (TVS diodes), varistors, and fuses near the input jack. These components sacrifice themselves to protect the inner circuitry from voltage spikes. bm5291 ver 1.3 schematic